• Korean Journal of Materials Research
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• v.10 no.8
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• pp.545-550
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• 2000

3Y-TZP, 12Ce-TZP 및 3Y-TZP, 12Ce-TZP 현탁액의 제타포텐셜과 겉보기점도의 측정으로부터 슬립주입공정에 의한 다층복합체의 제조조건을 조사하였다. 아울러 다층복합체의 소결밀도, 미세구조, 결정상에 미치는 열처리의 영향을 검토하였다. 3Y-TZP와 12Ce-TZP 현탁액의 등전점을 pH 8부근이었으나 3Y-TZP/12Ce-TZP의 등전점은 pH8.6이었다. 현탁액은 전단속도의 증가와 더불어 점도가 감소하는 의가소성유동을 나타내었다. 15 및 20vol% 고체함량을 갖는 3Y-TZP와 3Y-TZP/12Ce-TZP 현탁액은 소량(0.3wt%)의 유기해교제의 첨가만으로 슬립주입에 적당한 유동성을 보유하였으나, 12Ce-TZP의 경우는 점도를 감소시키기 위하여 부가적인 전해질이 필요하였다. 이론밀도의 98% 이상을 보유하고 0.3~$2.2\mu\textrm{m}$의 입경을 갖는 치밀한 다층복합체가$ 1500^{\circ}C$ 소결로 얻어졌다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.660-669
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• 1989

The strain distribution in a wide strip drawn through a wedge-shaped die is obtained from the numerical integration of strain increments along the flow path of material points in the slipline field for a non-hardening material under the plane strain condition. It is shown that the strain in the surface layer increases with friction and that the strain at the mid-plane is a function of area reduction only. The redundant deformation factor, obtained from the average strain in a drawn strip, increases with friction. For the workability analysis of a strip drawing process, the strain states along with hydrostatic stresses are needed for the evaluation of a damage function based on the hole-growth mechanism of ductile fracture. The critical maximum of the damage function is assumed to be a material constant. As a result, mid-plane cracking is likely to occur in a process at a small reduction, with a large die angle, and in poor lubrication. Distortions of an initially transverse line are also calculated.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.274-274
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• 2022

확률론적 지진해일 재해도 평가(PTHA)는 최근 지진해일에 대한 연구에서는 관심을 많이 받고 있는 주제로 여러 국가에서 연구가 진행되고 있다. 단층매개변수의 민감도 분석은 일본(Goda et al., 2014), 미국(Sepúlveda and Liu, 2016), 뉴질랜드(D. Burbridge et al., 2015) 등에서 연구가 활발하게 이루어졌으며 현재도 활발한 연구가 진행되고 있다. 민감도 분석은 PTHA를 진행하기 위한 선행 과정으로 파향선 추적을 통한 대상지 설정 및 연구 대상 단층을 선정한 후 로직트리를 만들기 위해 각 단층 매개변수의 범위와 단위 폭을 제시한다. 해당 연구는 세 가지 단층 매개변수에 대한 지진해일 초기파와 파고에 대한 민감도 분석을 실행했다. 주향각은 초기파와 지진해일고에 대해서 임의의 변동을 보이지만 변동 폭은 다른 두 매개변수들과 비교하여 가장 크다. 경사각과 슬립각은 단층의 수직 움직임을 변화시키며 이를 통해 초기파의 변동을 예측할 수 있다. 초기파의 변동과 모양을 분석함으로써 수치 계산이 가설과 유사한 결과를 보임을 확인하였다. 경사각과 슬립각에 의한 지진해일고의 변화는 최저 지진해일고가 초기파의 총 에너지와 연관된다는 결론에 이른다. 지진해일 재해도는 해안지역에 도달하는 최종 파고와 관련이 있으므로 각 매개변수의 단위 폭은 지진해일고의 결과를 통해 선정되었다. 민감도 분석은 제시한 주향각, 경사각, 슬립각의 단위 폭을 이용하여 로직트리의 분기 수를 감소시켜 수치 계산 시간을 줄임으로써 PTHA의 효율성을 증대시킨다.

• The KIPS Transactions:PartC
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• v.17C no.1
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• pp.1-14
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• 2010

IEEE 802.15.4[1] has been standardized for the physical layer and MAC layer of LR-PANs(Low Rate-Wireless Personal Area Networks) as a technology for operations with low power on sensor networks. The standardization is applied to the variety of applications in the shortrange wireless communication with limited output and performance, for example wireless sensor or virtual wire, but it includes vulnerabilities for various attacks because of the lack of security researches. In this paper, we analyze the vulnerabilities against the denial of sleep attacks on the MAC layer of IEEE 802.15.4, and propose a detection mechanism against it. In results, we analyzed the possibilities of denial of sleep attacks by the modification of superframe, the modification of CW(Contention Window), the process of channel scan or PAN association, and so on. Moreover, we comprehended that some of these attacks can mount even though the standardized security services such as encryption or authentication are performed. In addition to, we model for denial of sleep attacks by Beacon/Association Request messages, and propose a detection mechanism against them. This detection mechanism utilizes the management table consisting of the interval and node ID of request messages, and signal strength. In simulation results, we can show the effect of attacks, the detection possibility and performance superiorities of proposed mechanism.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.26 no.4
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• pp.397-405
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• 2008

The position accuracy is primarily dependent on the satellite position and signal delay caused by several elements. To know the effect of the delay on the estimated positions, we simulated GPS raw data (RINEX) with GPS errors using Bernese ver5.0. GPS errors used in this paper are Ionospheric delay, Cycle slip, Troposphere, DOP and Random error. If the baseline is short, the position error according to TEC is not large, since the ionospheric delay effect can be removed by ion-free combination. However, if the baseline is long, 3 dimensional position error up to 10cm is occurred. The 3D position error of coordinates with cycle slip is hardly ever changed up to 60% of cycle slip. Because the simulated cycle slips are equally distributed on satellites, the positioning was not seriously affected by the cycle slip. Also, if percentage of cycle slip is 60%, three dimensional error is sharply increased over 1m. The position error is calculated by using the observation data (2 hours) which was selected by DOP less than 3. And its accuracy is more improved about $3{\sim}4cm$.

• Journal of the Society of Disaster Information
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• v.16 no.4
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• pp.712-722
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• 2020

Purpose: The damage from earthquakes with a magnitude of 5.0 or greater Korea has increased in South Korea. When a earthquake occurs, internal facilities and electric equipment besides urban structures will be damaged. Thus, in this paper, an earthquake-induced seismic isolation device with double slip fiction surfaces which can reduce the damage of electric power equipment such as distribution panel and then the seismic performance was evaluated. Method: To evaluate the seismic performance shaking table test was performed, a seismic performance comparison was performed according to the presence or absence of a seismic isolation device. The attenuation effect of the seismic isolation device are analyzed by comparing response acceleration and displacement for different frequencies and acceleration levels. Result: As a result of the test, the acceleration amplification was up to 42% less than when the seismic isolation device was installed in comparison to the other case without the seismic device. This is believed that the amplification energy has reduced because the displacement between the double slip friction surfaces of the seismic device play a role in dissipating the seismic energy. Conclusion: The seismic device with double slip friction surfaces has a greater earthquake attenuation effect in strong earthquakes than in weak ones, so the greater the frequency, the better the earthquake attenuation effect. Therefore, it is judged that earthquake energy can be decreased by applying to electric equipment such as distribution panels.

• Proceedings of the KIEE Conference
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• 1983.07a
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• pp.70-72
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• 1983

• Transactions of The Korea Fluid Power Systems Society
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• v.4 no.1
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• pp.13-17
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• 2007

The brake gain adaptive wheel slip controller for a vehicle is designed in this paper. The brake gain from braking pressure to braking torque defined by friction coefficient, friction area and effective friction radius is estimated by the adaptive law based on the wheel slip dynamics. And the wheel slip controller is designed based on the estimated brake gain. The robustness of the designed controller is analyzed using Lyapunov function and the convergence of brake gain is verified. Proposed wheel slip controller is verified via CarSim simulation with two kinds of desired wheel slip ratio.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.1
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• pp.51-57
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• 2011

Information of the lateral velocity and the sideslip angle in a vehicle is very useful in many active vehicle safety applications such as yaw stability control and rollover prevention. Because cost-effective sensors to measure the lateral velocity and the sideslip angle are not available, reliable algorithms to estimation them are necessary. In this paper, a sliding mode observer is designed to estimate the lateral velocity. The side slip angle is estimated using the recursive least square with the disturbance observer and the pseudo integral. The estimated parameters from the combined estimation method are updated recursively to minimize the discrepancy between the model and the physical plant, and any possible effects caused by disturbances. The performance of the proposed monitoring system is evaluated through simulations and experiments.

• Journal of the Korean Society for Railway
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• v.11 no.2
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• pp.176-181
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• 2008

This paper presents results from experimental analysis of a friction-driven wheel responsible for generating wheel squeal noise. Squeal noise generating mechanism has been examined under the laboratory condition by the model rig on a small scale. Creep characteristics and squeal noise were observed by changing the possible variables, such as relative velocities and friction coefficients in time- and frequency-domain.